The present invention relates to novel spectral sensitizing dyes and their use as sensitizer in photographic materials.
Silver halide photographic light sensitive materials are required to have high sensitivity in the specific wavelength regions depending on purpose of use. As one method to obtain such silver halide photographic light sensitive materials, it is well known to add various kinds of cyanine dyes or merocyanine dyes to silver halide photographic emulsion to very effectively enhance sensitivity of the emulsion in a specific wavelength region in a longer wavelength region than the sensitive wavelength region peculiar to the silver halide.
When dyes are added in silver halide photographic emulsion, they have not only spectral sensitization effect, but also the following requirements must be satisfied:
(1) Spectral sensitization should be proper optical regions. (2) Stable photographic properties should be maintained during storage of light sensitive materials. (3) Stain or fog due to residual dye added for spectral sensitization should not be retained after development treatment. (4) There should be no unfavorable interaction with other photographic additives.
Although there have been known many cyanine dyes and merocyanine dyes containing benzoxazole ring, a few of them satisfy the above requirements such as sensitizability and photographic properties.